Extracting power from moving water

1. A prime mover, fixedly mounted in a current of a body of water on the bed of said body of water, for extracting power from the current of water comprising:

a body;

at least one hydroplane depending from the body, the angle of inclination of the hydroplane with respect to the current flow being operatively changeable by rotation of the hydroplane about an axis which axis passes through the body and which axis is substantially perpendicular to the direction of flow of the current, the hydroplane being operatively rotatable about said axis between: (a) first positions in which the angle of inclination is such that the action of the current on the hydroplane is effective to generate thrust in a first direction and thereby to move the body in said first direction, and (b) second positions in which the angle of inclination is such that the action of the current on the hydroplane is effective to generate thrust in a second direction opposite to the first direction and thereby to move the body in said second direction;

means for rotating the hydroplane from a said first position to a said second position when the body is moving in the first direction and for rotating the hydroplane from a said second position to a said first position when the body is moving in the second direction thereby causing the body to execute a controlled oscillation;

means for extracting power from the oscillatory movement of the body; and

computerised control means controlling said means for rotating the hydroplane, wherein the angle of the hydroplane is determined by said control means in accordance with at least one parameter selected from the group comprising the instantaneous position of the body, the speed of the current, the speed of the hydroplane, the direction of movement of the hydroplane, force applied to the hydroplane at a given instant by the current and the maximum achievable power output at a prevailing current speed.

2. An apparatus for extracting power from moving water comprising a prime mover according to claim 1 .

3. A method for extracting power from a current of water using a prime mover as claimed in claim 1 , comprising periodically reversing the direction of thrust generated by the said hydroplane.

4. A method of extracting power from a current of water comprising:

providing a prime mover adapted for submersion in a current of water comprising (a) a body having first and second hydroplanes mounted thereon and extending on respective sides thereof and (b) means for adjusting the angle of inclination of the hydroplanes with respect to the current flow;

adjusting the hydroplanes to a first position in which the angle of inclination with respect to the current is such that the action of the current on the hydroplanes is effective to generate thrust in a first direction and thereby to move the body in said first direction;

adjusting the hydroplanes to a second position in which the angle of inclination with respect to the current is such that the action of the current on the hydroplanes is effective to generate thrust in a second direction opposite to the first direction and thereby to move the body in said second direction, wherein the hydroplanes are adjusted from a said first position to a said second position when the body is moving in the first direction and the hydroplanes are adjusted from a said second position to a said first position when the body is moving in the second direction thereby causing the body to execute a controlled oscillation; and

extracting power from the oscillatory movement of the body.